Semiconductor device

1. A semiconductor device, comprising: a silicon carbide substrate including a main surface having an off angle with respect to a {0001} plane; and an ohmic electrode formed in contact with said main surface, a base surface being exposed at least a part of a contact interface of said silicon carbide substrate with said ohmic electrode, and wherein a length of said base surface in a direction of the off angle is not smaller than 36 nm and not greater than 430 nm.

2. The semiconductor device according to claim 1 , wherein said ohmic electrode contains at least one metal of Ni, Ti, and Al.

3. The semiconductor device according to claim 2 , wherein said ohmic electrode is composed of a TiAlSi alloy or an NiSi alloy.

4. The semiconductor device according to claim 1 , further comprising: an oxide film formed in contact with said silicon carbide substrate; a gate electrode formed in contact with said oxide film such that said oxide film lies between the gate electrode and said silicon carbide substrate; and a drain electrode formed in contact with said silicon carbide substrate, wherein said ohmic electrode is a source electrode, said source electrode and said drain electrode are configured such that a current which flows between said source electrode and said drain electrode can be controlled with a gate voltage applied to said gate electrode, a difference between a first threshold voltage of said semiconductor device which is measured first and a second threshold voltage of said semiconductor device which is measured after application of stress to said semiconductor device continuously for 1000 hours is within ±0.2 V, and application of said stress means application of said gate voltage of −15 V to said gate electrode while a voltage of said source electrode is 0 V and a voltage of said drain electrode is 0 V.